1. Field of the Invention
The present invention relates to a turbo-molecular pump equipped with a radiation temperature measuring apparatus capable of measuring the temperature of a measurement object based on infrared rays constituting heat energy radiated from the measurement object and improved in terms of accuracy in temperature measurement.
2. Description of the Related Art
With the recent development of electronics, there is a rapid increase in the demand for semiconductor devices such as memories and integrated circuits.
Such semiconductor devices are manufactured, for example, by doping a semiconductor substrate of very high purity with impurities to impart electrical properties thereto or by forming minute circuits on a semiconductor substrate through etching.
Furthermore, such manufacturing operation has to be conducted in a high-vacuum chamber in order to avoid the influence of dust, etc. in the air. To evacuate the chamber, a vacuum pump is generally used. In particular, as the vacuum pump, a turbo-molecular pump, which involves little residual gas and is easy to maintain, is widely used.
Further, a semiconductor manufacturing process involves a number of steps in which various process gases act on a semiconductor substrate, and the turbo-molecular pump is used not only to evacuate the chamber but also to discharge these process gases from the chamber. FIG. 6 is a longitudinal sectional view of the turbo-molecular pump.
In FIG. 6, a turbo-molecular pump 100 has at the upper end of an outer cylinder 127 an intake port 101. Inside the outer cylinder 127, there is provided a rotor 103 in the periphery of which a plurality of rotary blades 102a, 102b, 102c, . . . constituting turbine blades for sucking and discharging gas are formed radially in a number of stages.
Mounted at the center of the rotor 103 is a rotor shaft 113, which is supported so as to levitate and be positionally controlled by, for example, a so-called 5-axis control magnetic bearing.
An upper radial electromagnet 104 is composed of four electromagnets arranged in pairs in the X- and Y-axis directions. An upper radial sensor 107 composed of four electromagnets is provided in close vicinity to and in correspondence with the upper radial electromagnet 104. The upper radial sensor 107 detects radial displacement of the rotor 103 and sends the detection result to a control device (not shown).
Based on the displacement signal detected by the upper radial sensor 107, the control device controls the excitation of the upper radial electromagnet 104 through a compensation circuit with a PID adjusting function to adjust the upper radial position of the rotor shaft 113.
The rotor shaft 113 is formed of a material with high magnetic permeability (e.g., iron) or the like, and is attracted by the magnetic force of the upper radial electromagnet 104. Such adjustment is performed independently in the X- and Y-axis directions.
Further, a lower radial electromagnet 105 and a lower radial sensor 108 are arranged in the same manner as the upper radial electromagnet 104 and the upper radial sensor 107, adjusting the lower radial position of the rotor shaft 113 in the same manner as the upper radial position thereof.
Further, there are arranged axial electromagnets 106A and 106B, with a metal disc 111 provided on the lower portion of the rotor shaft 113 being therebetween. The metal disc 111 is formed of a material with high magnetic permeability such as iron. To detect axial displacement of the rotor shaft 113, there is provided an axial sensor 109, whose axial displacement signal is transmitted to the control device.
Furthermore, based on this axial displacement signal, the axial electromagnets 106A and 106B are excitation-controlled through the compensation circuit with PID adjusting function of the control device. The axial electromagnet 106A magnetically attracts the metal disc 111 upwardly, and the axial electromagnet 106B attracts the metal disc 111 downwardly.
In this way, the control device properly adjusts the magnetic force applied to the metal disc 111 by the axial electromagnets 106A and 106B to cause the rotor shaft 113 to magnetically levitate in the axial direction and to support it in a non-contact fashion.
A motor 121 is equipped with a plurality of magnetic poles circumferentially arranged so as to surround the rotor shaft 113. Each magnetic pole is controlled by the control device so as to rotate the rotor shaft 113 through an electromagnetic force acting between it and the rotor shaft 113.
Further, an RPM sensor 110 is mounted to the lower end of the rotor shaft 113. The control device detects the RPM of the rotor shaft 113 from a detection signal of the RPM sensor 110.
Further, in the vicinity, for example, of the lower radial sensor 108, there is mounted a phase sensor (not shown), which detects the rotation phase of the rotor shaft 113. By using the detection signals of the phase sensor and the RPM sensor 110, the control device detects the position of each magnetic pole.
A plurality of stationary blades 123a, 123b, 123c, . . . are arranged with slight gaps between the rotary blades 102a, 102b, 102c, . . . . The rotary blades 102a, 102b, 102c, . . . downwardly transfer the molecules of exhaust gas through collision. For this purpose, they are inclined by a predetermined angle from a plane perpendicular to the axis of the rotor shaft 113.
Similarly, the stationary blades 123 are inclined by a predetermined angle from a plane perpendicular to the axis of the rotor shaft 113, and are arranged alternately with the rotary blades 102 so as to extend toward the inner periphery of the outer cylinder 127.
Furthermore, each stationary blade 123 is supported, with its one end being inserted between a plurality of stationary blade spacers 125a, 125b, 125c, . . . stacked together.
The stationary blade spacers 125 are ring-like members formed, for example, of a metal, such as aluminum, iron, stainless steel, or copper, or an alloy containing some of these metals as the components.
In the outer periphery of the stationary blade spacers 125, there is secured in position the outer cylinder 127 with a slight gap therebetween. At the bottom of the outer cylinder 127, there is arranged a base portion 129, and a threaded spacer 131 is arranged between the lower portion of the stationary blade spacers 125 and the base portion 129. Additionally, formed in the lower portion of the threaded spacer 131 in the base portion 129 is an exhaust port 133, which communicates with the exterior.
The threaded spacer 131 is a cylindrical member formed of a metal, such as aluminum, copper, stainless steel, or iron, or an alloy containing some of these metals as the components, and has in its inner peripheral surface a plurality of spiral thread grooves 131a. 
The spiral thread grooves 131a are oriented such that when the molecules of exhaust gas move in the rotating direction of the rotor 103, these molecules are transferred to the exhaust port 133.
At the lowermost portion of the rotary blades 102a, 102b, 102c, . . . of the rotor 103, a rotary blade 102d extends vertically downwards. The outer peripheral surface of this rotary blade 102d is cylindrical and protrudes toward the inner peripheral surface of the threaded spacer 131 so as to be in close vicinity to the inner peripheral surface of the threaded spacer 131 with a predetermined gap therebetween.
The base portion 129 is a disc-like member forming the base portion of the turbo-molecular pump 100, and is generally formed of a metal such as iron, aluminum, or stainless steel.
The base portion 129 physically supports the turbo-molecular pump 100, and also serves as a heat conduction path, so that it is desirable for the base portion 129 to be formed of a metal, such as iron, aluminum, or copper, which has rigidity and high heat conductivity.
In this construction, when the rotary blades 102 are driven by the motor 121 to rotate with the rotor shaft 113, exhaust gas from a chamber is taken in through the intake port 101 by the action of the rotary blades 102 and the stationary blades 123.
The exhaust gas taken in through the intake port 101 flows between the rotary blades 102 and the stationary blades 123 and is transferred to the base portion 129. At this time, the temperature of the rotary blades 102 rises due to the frictional heat generated when the exhaust gas comes into contact with the rotary blades 102 and the conduction of the heat generated in the motor 121, and the heat thus generated is transmitted to the stationary blades 123 side through radiation or conduction by the molecules of the exhaust gas.
The stationary blade spacers 125 are joined together in the outer periphery thereof, and transmit to the exterior the heat received by the stationary blades 123 from the rotary blades 102, the frictional heat generated when the exhaust gas comes into contact with the stationary blades 123, etc.
The exhaust gas transferred to the base portion 129 is sent to the exhaust port 133 while being guided by the thread grooves 131a of the threaded spacer 131.
While in the above-described example the threaded spacer 131 is arranged in the outer periphery of the rotary blade 102d, and the thread grooves 131a are formed in the inner peripheral surface of the threaded spacer 131, it is also possible, in some cases, to form the thread grooves in the outer peripheral surface of the rotary blade 102d and to arrange in its periphery a spacer having a cylindrical inner surface.
Further, in order that the gas taken in through the intake port 101 may not enter the electrical component section constituted of the motor 121, the lower radial electromagnet 105, the lower radial sensor 108, the upper radial electromagnet 104, the upper radial sensor 107, etc., the electrical component section is covered with a stator column 122, and the interior of the electrical component section is maintained at a predetermined pressure by a purge gas.
For this purpose, piping (not shown) is arranged in the base portion 129, and the purge gas is introduced through this piping. The purge gas introduced is sent to the exhaust port 133 by way of the gap between a protective bearing 120 and the rotor shaft 113, the gap between the rotor and stator of the motor 121, and the gap between the stator column 122 and the rotary blades 102.
In some cases, to increase reactivity, the process gas is introduced into the chamber while at high temperature. And, when cooled to a certain temperature while being discharged, the process gas may solidify and deposit a product in the exhaust system.
Furthermore, in some cases, such process gas attains low temperature in the turbo-molecular pump 100 to solidify, adhering to the inner surfaces of the turbo-molecular pump 100 to be deposited thereon.
As can be seen from a vapor pressure curve, when, for example, SiCl4 is used as the process gas in an Al etching apparatus, a solid product (e.g., AlCl3) is deposited to adhere to the inner surfaces of the turbo-molecular pump 100 under low vacuum (760 [torr] to 10−2 [torr]) and at low temperature (approximately 20 [C]).
When a deposit substance from the process gas is deposited on the inner surfaces of the turbo-molecular pump 100, this substance narrows the pump flow passage, resulting in a deterioration in the performance of the turbo-molecular pump 100.
The solidification and adhesion of such product is likely to occur in the portion near the exhaust port, which is at low temperature, and, in particular, near the rotary blades 102 and the threaded spacer 131. This has conventionally been coped with by winding a heater, a water-cooling tube, etc. (not shown) around the base portion 129, etc., and embedding a temperature sensor (e.g., thermistor) (not shown) in, for example, the base portion 129, maintaining the base portion 129 at a fixed temperature based on a signal from this temperature sensor through heating by the heater or cooling by the water-cooling tube (which is hereinafter referred to as TMS (temperature management system)).
Prior to normal operation of the turbo-molecular pump 100, the turbo-molecular pump 100, the semiconductor manufacturing apparatus, and the piping connecting them are heated at temperature over fixed one for a fixed period of time for degassing (hereinafter referred to as baking). Then, they are restored to room temperature, whereby it is possible to increase the degree of vacuum of the interior of the intake port of the turbo-molecular pump 100 and the interior of the chamber (which leads to an improvement in so-called ultimate pressure).
When the temperature of the rotary blades 102 of the turbo-molecular pump 100 exceeds the long-term permissible heat-resistant temperature (which is 150 [C] when the rotary blades are formed of an aluminum alloy), the turbo-molecular pump is affected by heat, and mainly the rotary blades 102 undergo a deterioration in strength, suffering breakage in the worst case.
The higher the set temperature of the TMS, the less likely the deposition of the product. Thus, it is desirable for the set temperature to be as high as possible. However, raising this set temperature results in a rise of the temperature of the portion around the rotary blades 102, which hinders heat dissipation of the rotary blades 102. As a result, the temperature of the rotary blades 102 rises, so that there is a fear of the service life of the rotary blades 102 being shortened and their suffering breakage or the like.
Similarly, the higher the baking temperature, the more improvement in ultimate pressure. Thus, it is desirable for the baking temperature to be as high as possible. However, when the baking temperature is too high, the temperature of the rotary blades 102 rises, so that there is a fear of the service life of the rotary blades 102 being shortened due to the heat.
Thus, it is desirable to monitor the temperature of the rotary blades 102. Conventionally, as shown, for example, in FIG. 6, a radiation thermometer 141 is embedded in the base portion 129, and directed to the bottom surface of the rotary blade 102d. However, the monitoring of the temperature of the rotary blade 102d involves the following inconvenience.
The portion of the base portion 129 in which the radiation thermometer 141 is embedded is susceptible to product deposition, which means the accuracy in temperature measurement is likely to be affected by the product.
Further, the radiation thermometer 141 is designed such that the closer to 1 the emissivity of the measurement object, the more accurate the measurement.
However, the material of the rotary blades 102 generally includes an aluminum alloy with nickel plating, etc. so that the emissivity of the blade surfaces is as low as 0.1 or less, resulting in a rather poor measurement accuracy.
Further, with respect to the measurement object, there exists a view angle (angle α in FIG. 7) for the radiation thermometer 141 within which measurement is possible. And, when, as shown in FIG. 7, the surface constituting the measurement object is the bottom surface of the rotary blade 102d, it is subject to the influence of backlight, and radiation heat from a non-measurement object outside the measurement region indicated by the view angle α, such as the base portion 129, enters the radiation thermometer 141 directly or after being reflected, resulting in a rather poor measurement accuracy.